WO2018193496A1

WO2018193496A1 - Radio terminal, base station, radio communication system, and radio communication method

Info

Publication number: WO2018193496A1
Application number: PCT/JP2017/015472
Authority: WO
Inventors: 横山　仁
Original assignee: 富士通株式会社
Priority date: 2017-04-17
Filing date: 2017-04-17
Publication date: 2018-10-25
Also published as: JP6954344B2; JPWO2018193496A1; US20200045591A1

Abstract

A radio terminal comprises: a storage unit that stores first line identification information used for identifying line setting information related to the communication line between a base station and a core network during a first state in which the radio line between the radio terminal and a plurality of base stations is disconnected and in which the communication line between one of the plurality of base stations that is used for the radio terminal to communicate via that base station and the core network is maintained, the storage unit further storing base station identification information used for identifying a first base station providing a cell in which the radio terminal awaits radio signals; and a control unit that, in a case of changing the cell for another in which to await the radio signals when the radio terminal is in the first state, transmits, via a radio processing unit, the first line identification information and the base station identification information to a second base station providing the other cell and then stores, into the storage unit, second line identification information received from the second base station and used for identifying line setting information.

Description

Wireless terminal, base station, wireless communication system, and wireless communication method

The present invention relates to, for example, a wireless terminal, a base station, a wireless communication system, and a wireless communication method that perform wireless communication.

In a wireless communication system such as a mobile communication system, a discontinuous reception (DRX) function is adopted to reduce power consumption of a wireless terminal. For example, in Long Term Evolution (LTE), which is one of the wireless communication standards for mobile communication, a wireless terminal is set at a preset time for each preset period (referred to as DRX period) for each wireless terminal. Wake up in a section (for example, subframe) (or become active or enter standby). The radio terminal demodulates and decodes the radio resource allocation information (scheduling information) to be transmitted in the wake-up time interval. Then, the wireless terminal refers to the scheduling information and confirms whether there is an incoming call addressed to the local station based on the presence / absence of resources allocated to the local station. On the other hand, outside the set time interval, the wireless terminal turns off the operation of the portion that performs such demodulation processing and decoding processing in the circuit that performs wireless communication processing to reduce power consumption.

In addition, in the study of the specifications of the so-called 5th generation mobile communication system by the 3GPP working group, Inactive state was added as one of Radio Resource Control (RRC) state so that it can cope with a longer period of suspension than DRX. It has been proposed to do. The fifth generation mobile communication system is a standard for mobile communication after LTE and LTE-Advanced.

In RRC Inactive state, the core network line established between the base station and the upper node (hereinafter referred to as the upper line) is maintained without being disconnected even during the period when the wireless terminal is not communicating. (Set). On the other hand, the wireless line between the base station and the wireless terminal is disconnected (for example, see Non-Patent Document 1). Note that the state where both the upper line and the wireless line are set is called RRC connected state (or RRC connected), and the state where both the upper line and the wireless line are disconnected is RRC connected state (or idle). Called). RRC Inactive state can be interpreted as a state located between RRC Connected state and RRC Idle state.

In RRC Inactive state, communication settings are resumed by storing channel setting information for wireless terminals to communicate via the base station and using the stored line setting information when the wireless terminals resume communication. A Resume function has been proposed that can omit part of the communication of control information at the time. Regarding the Resume function, the stored line setting information is managed in association with, for example, identification information (hereinafter referred to as Resume ID). Therefore, when the wireless terminal resumes communication, the Resume ID is transmitted between the wireless terminal and the base station, and the wireless terminal uses the circuit setting information corresponding to the same Resume ID so that the wireless terminal can communicate. Can be resumed. In addition, by using the line setting information and the Resume ID, the communication amount of control information required when communication is resumed is reduced.

Therefore, by introducing RRCRRInactive state, for example, a device that communicates once a day or less frequently, such as a wireless terminal used in the so-called Internet of Things (Internet of Things, IoT) It is expected to reduce power consumption.

However, there may be a situation where it is preferable to change the cell in which the wireless terminal waits for a wireless signal addressed to itself while the wireless terminal is in the RRC Inactive state and has stopped communication. Hereinafter, a cell in which a wireless terminal waits for a radio signal addressed to itself is simply referred to as a standby cell (also referred to as a camp-on-cell). In such a case, it is preferable that the line setting information maintained for the wireless terminal is handed over to the base station that provides the changed standby cell.

In one aspect, the present invention provides a wireless communication system capable of maintaining line setting information for a wireless terminal even when the standby cell of the wireless terminal is changed during a period in which the wireless terminal stops communication. The purpose is to provide a terminal.

According to one embodiment, a wireless terminal is provided. The wireless terminal transmits a wireless signal to any of a plurality of base stations providing a cell or receives a wireless signal from any of the plurality of base stations, and between the wireless terminal and each base station In a first state in which the wireless line is disconnected and the communication line between the base station and the core network used for the wireless terminal to communicate via any of the plurality of base stations is maintained. First line identification information for identifying line setting information on a communication line between the base station and the core network, and a first base that provides a cell in which a wireless terminal waits for a radio signal among a plurality of base stations A storage unit that stores base station identification information for identifying a station, and first line identification information and base station identification information when a cell that waits for a radio signal is changed when the wireless terminal is in the first state. And the wireless processor It transmits to the second base station providing the cell after the change over, and a control unit for storing the second line identification information received from the second base station in the storage unit.

According to another embodiment, a base station that provides a cell is provided. The base station transmits a radio signal to the radio terminal or receives a radio signal from the radio terminal, a communication interface unit for connecting to an upper node or another base station, and a radio from the radio terminal Via the processing unit, base station identification information for identifying other base stations, and the radio link between the radio terminal and the other base station is disconnected, and the radio terminal communicates via the other base station. First for identifying line setting information about a communication line between another base station and the core network in a first state in which a communication line between the other base station and the core network used for maintenance is maintained The first line identification information is transmitted to the other base station identified by the base station identification information via the communication interface unit, and from the other base station via the communication interface unit. A control unit that receives line setting information corresponding to one line identification information, associates the second line identification information with the line setting information, and transmits the second line identification information to the wireless terminal via the wireless processing unit. And have.

According to another embodiment, a base station that provides a cell is provided. This base station is used for communication with a host node or another base station, a radio line between the radio terminal and the base station is disconnected, and the radio terminal communicates via the base station. A memory for storing the line setting information about the communication line between the base station and the core network in the first state in which the communication line between the base station and the core network is maintained in association with the first line identification information And a control unit that, when receiving the first line identification information from another base station through the communication interface unit, transmits the line setting information to the other base station through the communication interface unit.

According to still another embodiment, a wireless communication system having a plurality of base stations that provide cells and wireless terminals is provided. In this wireless communication system, a wireless terminal is used for disconnecting a wireless link between the wireless terminal and each of the plurality of base stations, and for the wireless terminal to communicate via any of the plurality of base stations. When a cell waiting for a radio signal is changed from the first cell to the second cell when the communication line between the station and the core network is maintained in the first state, A plurality of base station identification information for identifying a first base station that provides a first cell, and first line identification information for identifying line setting information for a communication line between the base station and the core network. To the second base station that provides the second cell of the base stations.
When the second base station transmits the first line identification information to the first base station and receives the line setting information from the first base station, the second base station sends the second line identification information to the line setting information. At the same time, the second line identification information is notified to the wireless terminal.

According to still another embodiment, a radio communication method in a radio communication system having a plurality of base stations that provide cells and radio terminals is provided. In this wireless communication method, a wireless terminal disconnects a wireless link between a wireless terminal and each of a plurality of base stations, and the base station used for the wireless terminal to communicate via any of the plurality of base stations. When a cell waiting for a radio signal is changed from the first cell to the second cell when the communication line between the station and the core network is maintained in the first state, A plurality of base station identification information for identifying a first base station that provides a first cell, and first line identification information for identifying line setting information for a communication line between the base station and the core network. The first base station transmits the first line identification information to the first base station by the second base station, and transmits the first line identification information to the first base station. To the second base station for the first line identification information. The second base station associates the second line identification information with the received line setting information and notifies the wireless terminal of the second line identification information. .

The wireless terminal disclosed in this specification can maintain the line setting information about the wireless terminal even when the standby cell of the wireless terminal is changed during the period in which the wireless terminal stops communication .

FIG. 1 is a schematic configuration diagram of a wireless communication system according to an embodiment. FIG. 2 is a sequence diagram of processing relating to takeover of line setting information according to an example. FIG. 3 is a schematic configuration diagram of the base station. FIG. 4 is an operation flowchart of the target base station in the line setting information takeover process. FIG. 5 is an operation flowchart of the source base station in the line setting information takeover process. FIG. 6 is a schematic configuration diagram of a wireless terminal. FIG. 7 is an operation flowchart of the wireless terminal regarding the line setting information takeover process. FIG. 8 is a schematic configuration diagram of a radio communication system according to a modification. FIG. 9 is a sequence diagram of processing relating to takeover of line setting information according to a modification. FIG. 10 is a schematic configuration diagram of an aggregation station. FIG. 11 is a schematic configuration diagram of a distribution station. FIG. 12 is an operation flowchart of the wireless terminal regarding the handover process of line setting information according to a modification. FIG. 13 is a sequence diagram of processing relating to handover of line setting information according to a further modification. FIG. 14 is an operation flowchart of the target aggregation station in the line setting information takeover process according to a further modification. FIG. 15 is an operation flowchart of the wireless terminal in the handover process of line setting information according to a further modification.

Hereinafter, a wireless communication system, a base station, a wireless terminal, and a wireless communication method used in the wireless communication system will be described with reference to the drawings. This wireless communication system is compatible with the Resume function, and manages the line setting information maintained by the Resume function by adding Resume ID, which is identification information thereof. When the wireless terminal changes the standby cell while the wireless terminal is in the RRC-inactive state, the wireless terminal provides the current standby cell to the target base station that provides the changed standby cell. The source base station identification information and Resume ID are notified. When the target base station receives the Resume ID and the identification information of the source base station from the wireless terminal, the target base station notifies the source base station of the Resume ID and receives line setting information corresponding to the Resume ID from the source base station. Then, the target base station uses the received line setting information to establish an upper line for the wireless terminal, assigns a Resume ID to the wireless terminal, and notifies the wireless terminal of the assigned Resume ID. Thereby, even if the standby cell of the wireless terminal is changed while the wireless terminal stops communication, the wireless communication system transmits the line setting information maintained for the wireless terminal from the source base station to the target base station. You can take over to the station.

Note that the line setting information includes, for example, information related to Authentication, Security, and Context. The information related to Authentication includes, for example, information related to authorization of SIM information of the wireless terminal. Also, the information related to Security includes, for example, information related to encryption settings used in data communication related to wireless terminals. The information related to the context includes, for example, information related to Quality of Service (QoS) setting.

In this specification, Node B, eNode B, gNode B, or an access point is an example of a base station. Further, a mobile station, a mobile terminal, or User Equipment (UE) is an example of a wireless terminal.

FIG. 1 is a schematic configuration diagram of a wireless communication system according to one embodiment. The wireless communication system 1 includes two base stations 11-1 and 11-2, a wireless terminal 12, and an upper node 13. The base stations 11-1 and 11-2 and the wireless terminal 12 transmit signals to each other through wireless communication. Note that the number of base stations included in the wireless communication system 1 is not limited to two, and the wireless communication system 1 may include three or more base stations. Similarly, the wireless communication system 1 may include a plurality of wireless terminals 12 or may include a plurality of upper nodes 13. Further, when the wireless communication system 1 includes a plurality of upper nodes 13, the upper node to which the base station 11-1 is connected may be different from the upper node to which the base station 11-2 is connected. Further, the wireless terminal 12 may be a mobile terminal or a fixed communication device.

The base station 11-1 and the base station 11-2 relay communication between the wireless terminal 12 and the upper node 13. For this purpose, the base station 11-1 and the base station 11-2 are connected to the upper node 13 in accordance with a predetermined communication standard defined for communication between the upper node 13 and the base station, for example, an S1 interface. Further, the base station 11-1 and the base station 11-2 may be connected to each other or to other base stations in accordance with a predetermined communication standard defined for communication between base stations, for example, an X2 interface. .

Each of the base station 11-1 and the base station 11-2 provides one or more cells. For example, if the wireless terminal 12 is located in any cell set by the base station 11-1, the wireless terminal 12 can wirelessly communicate with the base station 11-1. Then, the base station 11-1 executes a procedure for setting a radio channel and a procedure for setting an upper channel such as a random access procedure and context setup with the radio terminal 12 capable of radio communication. Thereafter, the base station 11-1 receives a communication signal addressed to the wireless terminal 12 from the upper node 13 and transmits it to the wireless terminal 12 as a downlink wireless signal. Further, the base station 11-1 receives an uplink radio signal from the radio terminal 12, extracts a communication signal included in the radio signal to another communication device (not shown), and sends it to the upper node 13 Send a communication signal. Similarly, when the wireless terminal 12 is located in any cell set by the base station 11-2, the base station 11-2 transmits a downlink wireless signal to the wireless terminal 12, or An uplink radio signal is received from the terminal 12.

When the wireless terminal 12 is located in any cell set by the base station 11-1 and the base station 11-1 is a source base station, the base station 11-1 While in RRC connected state, execute processing related to Resume setting. That is, the base station 11-1 attaches Resume ID to the line setting information related to the wireless terminal 12 so that the wireless terminal 12 can use the Resume function. The base station 11-1 stores the line setting information together with the corresponding Resume ID. Further, the base station 11-1 transmits the Resume ID to the radio terminal while the radio terminal 12 continues the radio communication with the base station 11-1, that is, while the radio terminal 12 is in the RRC status “Connected” state. 12 is notified. Similarly, when the wireless terminal 12 is located in any cell set by the base station 11-2 and the base station 11-2 is a source base station, the base station 11-2 relates to the wireless terminal 12. Add Resume ID to the line setting information. The base station 11-2 stores the line setting information together with the corresponding Resume ID. Further, the base station 11-2 notifies the wireless terminal 12 of the Resume ID while the wireless terminal 12 is in the RRC connected state.

Thereafter, when the wireless terminal 12 determines to change the standby cell, the base station 11-1 and the base station 11-2 execute processing relating to the takeover of the line setting information. The details of the process related to the handover of the line setting information will be described later.

The wireless terminal 12 is a wireless terminal that can use the Resume function. For example, after the upper line and the wireless line are set in the RRC “Connected” state, the communication is stopped in the RRC “Inactive” state. That is, even if the radio line between the radio terminal 12 and the base station 11-1 or the base station 11-2 is disconnected, the upper level line related to the radio terminal 12 is maintained. The channel setting information for the wireless terminal 12 is held and managed by the base station 11-1 or the base station 11-2. The wireless terminal 12 reconnects the wireless line when a certain period (for example, several hours, several days, one month, etc.) or a specific event occurs, and uses the stored line setting information. Communication with another communication device (not shown) is resumed.

The upper node 13 includes, for example, Serving Gateway (S-GW), Mobility Management Entity (MME), and Packet data network Gateway (P-GW), and controls or data of the base station 11-1 or the base station 11-2. Establish a core network line for communication. Further, the upper node 13 executes control related to location registration of the wireless terminal 12 and handover between base stations, and executes control related to QoS and control related to charging. The upper node 13 executes control related to the upper line such as establishment or deletion of a bearer.

The details of the processing related to the transfer of line setting information will be described below. For example, when the wireless quality of another cell is better than the wireless quality of the current standby cell for the wireless terminal 12, processing related to taking over the line setting information is executed.

FIG. 2 is a sequence diagram of processing related to handover of line setting information according to an example. In this example, it is assumed that the base station 11-1 is a source base station and the base station 11-2 is a target base station. Also, Resume ID assigned to the line setting information of the wireless terminal 12 by the base station 11-1 is Resume ID1, and Resume ID assigned by the base station 11-2 to the line setting information of the wireless terminal 12 is Resume ID2.

After the line setting for the wireless terminal 12 is performed during the RRC connected state, and Resume ID1 is assigned to the line setting information, the wireless terminal 12 proceeds to RRC Inactive state (step S101).

After transitioning to RRC Inactive state, the radio terminal 12 sets the radio quality of the current standby cell set by the base station 11-1 and the radio quality of the cell set by the base station 11-2 to a certain period or not. Measure regularly. If the wireless terminal 12 determines that the wireless quality of the cell set by the base station 11-2 is better than the wireless quality of the current standby cell, the wireless terminal 12 determines to reselect the cell (step S102). ). Then, the radio terminal 12 changes the standby cell from the cell provided by the base station 11-1 to the cell provided by the base station 11-2.

When the radio terminal 12 determines to reselect the cell, the radio terminal 12 executes a random access procedure for the base station 11-2 which is the target base station. That is, the wireless terminal 12 refers to the identification information of the base station 11-2 indicated by the broadcast information from the base station 11-2. Then, the radio terminal 12 transmits Message 1 including the RA preamble to the base station 11-2 using the radio resource for physical random access (Physical Random Access Channel, CHPRACH) indicated by the broadcast information (step S1). S103). When the base station 11-2 detects the RA preamble, the base station 11-2 transmits an RA response as response information to the wireless terminal 12 as Message 2 (step S104). The RA response includes Timing 含む Advance (TA) information for adjusting the timing at which the radio terminal 12 transmits an uplink signal. The wireless terminal 12 refers to the TA information, and establishes strict synchronization with the base station 11-2 in terms of time. Then, the wireless terminal 12 receives the uplink (Up Link, UL) Scheduling から Grant from the base station 11-2. UL Scheduling Grant includes information indicating an uplink resource block assigned to the wireless terminal 12.

Based on the UL Scheduling Grant, the wireless terminal 12 sends Resume ID1 and the identification information of the base station 11-1 that is the source base station to the base station 11-2 as a Message 3 along with a connection request signal (Radio Resource Control Control connection Request). Transmit (step S105). The cell identification information (cell ID) provided by the base station is an example of base station identification information.

Upon receiving Resume１１ID1 and Message 3 including the identification information of the base station 11-1, the base station 11-2 refers to the identification information of the base station 11-1 and transmits Resume ID1 to the base station 11-1. Inquires about the line setting information of the wireless terminal 12 (step S106). Note that, when the base station 11-1 and the base station 11-2 are connected to each other via the X2 interface, the base station 11-2 does not go through the upper node 13 but goes to the base station 11-1. Resume ID1 may be sent directly. On the other hand, when the base station 11-1 and the base station 11-2 are connected to different upper nodes, the base station 11-2 transmits Resume ID1 to the base station 11-1 via the upper node. To do.

Upon receiving Resume１１ID1 assigned to the wireless terminal 12 from the base station 11-2, the base station 11-1 returns the line setting information of the wireless terminal 12 stored in association with the Resume ID1 to the base station 11-2. (Step S107). At this time, when the base station 11-1 and the base station 11-2 are connected to each other via the X2 interface, the base station 11-1 does not go through the upper node 13 but the base station 11-2. The line setting information may be sent directly to. On the other hand, when the base station 11-1 and the base station 11-2 are connected to different upper nodes, the base station 11-1 sends the line setting information to the base station 11-2 via the upper node. Send.

In addition, the base station 11-1 executes processing for releasing the upper line set for the wireless terminal 12 with the upper node 13 (step S108). Furthermore, the base station 11-1 also releases Resume ID1 assigned to the wireless terminal 12 (step S109).

On the other hand, when the base station 11-2 receives the channel setting information of the wireless terminal 12 from the base station 11-1, the base station 11-2 assigns Resume ID2 to the wireless terminal 12 (step S110). The base station 11-2 stores ResumeReID2 along with the channel setting information of the wireless terminal 12. Further, the base station 11-2 sets an upper line for the wireless terminal 12 based on the line setting information of the wireless terminal 12 (step S111). That is, the base station 11-2 establishes a core network line with the upper node 13 for the wireless terminal 12. Then, the base station 11-2 transmits Message 4 of the random access procedure including Resume ID2 to the wireless terminal 12 (step S112). The wireless terminal 12 stores the notified Resume ID2. Then, the base station 11-1, the base station 11-2, and the wireless terminal 12 end the line setting information takeover process.

Thereafter, when the wireless terminal 12 resumes communication, the wireless terminal 12 transmits Resume ID2 to the base station 11-2, and the base station 11-2 uses the line setting information corresponding to Resume ID2, Communication between the wireless terminal 12 and the core network may be resumed.

Hereinafter, details of the base station 11-1, the base station 11-2, and the wireless terminal 12 will be described. Since the configuration and function of the base station 11-1 and the configuration and function of the base station 11-2 can be the same, the base station 11-1 will be described below.

FIG. 3 is a schematic configuration diagram of the base station 11-1. The base station 11-1 includes an antenna 21, a wireless processing unit 22, a wired interface unit 23, a storage unit 24, and a control unit 25. The wireless processing unit 22, the storage unit 24, and the control unit 25 are formed as separate circuits. Alternatively, each of these units may be mounted on the base station 11-1 as one or a plurality of integrated circuits in which circuits corresponding to the respective units are integrated.

The antenna 21 transmits the downlink signal transmitted via the wireless processing unit 22 as a wireless signal. The antenna 21 receives a radio signal including an uplink signal from the radio terminal 12 and converts it into an electric signal, and transmits the electric signal to the radio processing unit 22 as an uplink signal. Note that the antenna 21 may have a transmitting antenna and a receiving antenna separately.

The radio processing unit 22 converts the downlink signal received from the control unit 25 into an analog signal, and then superimposes it on a carrier wave having a radio frequency designated by the control unit 25. The radio processing unit 22 amplifies the downlink signal superimposed on the carrier wave to a desired level by a high power amplifier (not shown), and transmits the downlink signal to the antenna 21.

The radio processing unit 22 amplifies the uplink signal received from the antenna 21 by a low noise amplifier (not shown). The radio processing unit 22 converts the frequency of the uplink signal from a radio frequency to a baseband frequency by multiplying the amplified uplink signal by a periodic signal having an intermediate frequency. Then, the radio processing unit 22 performs analog / digital conversion on the uplink signal having the baseband frequency, and then passes it to the control unit 25.

The wired interface unit 23 is an example of a communication interface unit, and includes a communication interface circuit for connecting the base station 11-1 to the upper node 13 and other base stations. The wired interface unit 23 analyzes the signal received from the upper node 13 according to the S1 interface that is a protocol between the upper node and the base station, and extracts a downlink signal, a control signal, and the like included in the signal. Further, the wired interface unit 23 analyzes a signal received from another base station in accordance with an X2 interface that is a protocol between adjacent base stations, and extracts a control signal, line setting information, or Resume ID included in the signal. . The wired interface unit 23 passes the extracted downlink signal and control signal to the control unit 25.

On the other hand, the wired interface unit 23 converts the uplink signal received from the control unit 25 into a signal in a format according to the S1 interface, and then outputs the signal to the upper node 13. The wired interface unit 23 converts the control signal, line setting information, or Resume ID transmitted to another base station into a format according to the X2 interface. Then, the wired interface unit 23 outputs (or transmits or notifies) the control signal to another base station.

The storage unit 24 includes, for example, a rewritable nonvolatile semiconductor memory or volatile semiconductor memory. The storage unit 24 stores various information (including identification information of the base station 11-1) for communicating with the wireless terminal 12, various information transmitted or received by the base station 11-1, and the base station 11- 1 stores various programs that operate in 1. Furthermore, the memory | storage part 24 memorize | stores the information regarding the Resume function about the radio | wireless terminal connected with the own station, ie, line | wire setting information, and Resume ID.

The control unit 25 includes, for example, one or a plurality of processors and their peripheral circuits. And the control part 25 modulates and multiplexes a downlink signal according to the modulation and multiplexing system employ | adopted by the communication standard with which the radio | wireless communications system 1 is based. Then, the control unit 25 passes the modulated and multiplexed downlink signal to the radio processing unit 22. For example, the control unit 25 modulates and multiplexes the downlink signal according to F-OFDM.

On the other hand, the control unit 25 separates the uplink signal received from the wireless processing unit 22 in accordance with the modulation and multiplexing method adopted by the communication standard that the wireless communication system 1 complies with, and demodulates the separated received signal. For example, the control unit 25 separates and demodulates the uplink signal according to F-OFDM. Then, the control unit 25 outputs the demodulated uplink signal to the wired interface unit 23. Further, the control unit 25 extracts various signals referred to by the base station 11-1 from the demodulated uplink signal, for example, control information related to call control or communication quality measurement information in the radio terminal 12.

Also, the control unit 25 executes various processes for executing wireless communication such as transmission power control and call control. Further, the control unit 25 attaches Resume ID to the line setting information obtained by performing the line setting process for the wireless terminal 12.

Further, when the base station 11-1 takes over the line setting information from another base station (for example, the base station 11-2) as the target base station for the wireless terminal 12, the control unit 25 performs the line setting information takeover process. Perform processing of the target base station. In addition, when the base station 11-1 serves as a source base station for the wireless terminal 12, the control unit 25 takes over the line setting information when passing the line setting information to another base station (for example, the base station 11-2). The processing of the source base station in is performed.

FIG. 4 is an operation flowchart of the target base station in the line setting information takeover process.

The control unit 25 determines whether or not the Message 3 of the random access procedure received from the wireless terminal 12 includes Resume ID1 assigned to the wireless terminal 12 by the source base station and the identification information of the source base station (Step S201). ). If Resume ID1 and source base station identification information are not included (step S201—No), the control unit 25 continues the random access procedure for the wireless terminal 12 (step S202).

On the other hand, if Resume ID1 and the identification information of the source base station are included (step S201—Yes), the control unit 25, via the wired interface unit 23, identifies the source base station specified by the identification information of the source base station. Resume ID1 is transmitted to (step S203). Thereby, the control unit 25 inquires of the source base station about the line setting information corresponding to ResumeReID1. Then, the control unit 25 receives line setting information corresponding to Resume ID1 from the source base station via the wired interface unit 23 (step S204).

Upon receiving the line setting information, the control unit 25 establishes a core network line (that is, an upper line) between the upper node 13 and the base station 11-1 for the wireless terminal 12 by using the line setting information ( Step S205). Further, the control unit 25 allocates Resume ID2 to the wireless terminal 12, and stores the Resume ID2 in the storage unit 24 together with the line setting information received (Step S206).

The control unit 25 generates a Message 4 of the random access procedure including the Resume ID 2 and transmits the Message 4 to the wireless terminal 12 as a radio wave via the wireless processing unit 22 and the antenna 21 (Step S207). After step S202 or step S207, the control unit 25 ends the operation of the target base station in the line setting information takeover process. In addition, the control part 25 may replace the order of the process of step S205 and the process of step S206, or may perform the process of step S205 and the process of step S206 in parallel.

FIG. 5 is an operation flowchart of the source base station in the line setting information takeover process.
The control unit 25 receives Resume ID1 from the target base station via the wired interface unit 23 (step S301). The control unit 25 refers to the storage unit 24 and identifies the line setting information corresponding to the received Resume ID1 (step S302).

Then, the control unit 25 transmits the specified line setting information to the target base station via the wired interface unit 23 (step S303). Further, the control unit 25 releases the communication line (that is, the upper line) between the base station 11-1 and the core network for the wireless terminal 12 set by the line setting information corresponding to Resume ID1, and Resume ID1 Is released (step S304). Then, the control unit 25 ends the operation of the source base station in the line setting information takeover process.

FIG. 6 is a schematic configuration diagram of the wireless terminal 12. The wireless terminal 12 includes an antenna 31, a wireless processing unit 32, a storage unit 33, and a control unit 34. Furthermore, the wireless terminal 12 may include one or more of a user interface (not shown) such as a touch panel, a microphone (not shown), a speaker (not shown), and a camera (not shown). . Furthermore, the wireless terminal 12 may have a Global Positioning System (GPS) receiver (not shown) in order to measure the position of the wireless terminal 12. The wireless processing unit 32, the storage unit 33, and the control unit 34 are formed as separate circuits. Alternatively, each of these units may be mounted on the wireless terminal 12 as one or a plurality of integrated circuits in which circuits corresponding to the respective units are integrated.

The antenna 31 transmits the uplink signal transmitted via the wireless processing unit 32 as a wireless signal. The antenna 31 receives a radio signal from the base station 11-1 or the base station 11-2, converts it into an electrical signal, forms a downlink signal, and transmits the downlink signal to the radio processing unit 32. Note that the antenna 31 may have a transmitting antenna and a receiving antenna separately.

The radio processing unit 32 analogizes the uplink signal received from the control unit 34 and then superimposes the uplink signal on a carrier wave having a radio frequency specified by the control unit 34. Then, the wireless processing unit 32 amplifies the uplink signal superimposed on the carrier wave to a desired level by a high power amplifier (not shown), and transmits the uplink signal to the antenna 31.

The wireless processing unit 32 amplifies the downlink signal received from the antenna 31 by a low noise amplifier (not shown). The radio processing unit 32 converts the frequency of the downlink signal from a radio frequency to a baseband frequency by multiplying the amplified downlink signal by a periodic signal having an intermediate frequency. Then, the wireless processing unit 32 performs analog / digital conversion on the downlink signal having the baseband frequency, and then passes it to the control unit 34.

The storage unit 33 includes, for example, a rewritable nonvolatile semiconductor memory or volatile semiconductor memory. The storage unit 33 stores various types of information for communicating with the base station 11-1 or the base station 11-2 (for example, identification information of a base station that can be received by the wireless terminal 12), and the wireless terminal 12 Stores various data transmitted or received. The storage unit 33 stores various programs that operate on the wireless terminal 12. Furthermore, the memory | storage part 33 memorize | stores the information regarding Resume function, ie, Resume ID.

The control unit 34 includes, for example, one or a plurality of processors and their peripheral circuits. And the control part 34 modulates and multiplexes an uplink signal according to the modulation and multiplexing system employ | adopted by the communication standard with which the radio | wireless communications system 1 is based. Then, the control unit 34 passes the modulated and multiplexed uplink signal to the radio processing unit 32. For example, the control unit 34 modulates and multiplexes the uplink signal in accordance with a multiplexing scheme according to F-OFDMA.

On the other hand, the control unit 34 separates the downlink signal received from the wireless processing unit 32 in accordance with the modulation and multiplexing method adopted by the communication standard that the wireless communication system 1 complies with, and demodulates the separated received signal. For example, the control unit 34 separates and demodulates the downlink signal according to F-OFDM. Then, the control unit 34 extracts various control information or data included in the demodulated reception signal. And the control part 34 performs the process according to the taken-out control information or data. For example, when an audio signal is included in the downlink signal, the control unit 34 reproduces the audio signal via a speaker. In addition, when the downlink signal includes a video signal, the control unit 34 reproduces the video signal via the touch panel.

Further, the control unit 34 executes various processes for executing wireless communication with the base station 11-1 or the base station 11-2, such as a connection request process. Further, the control unit 34 performs processing for measuring the quality of the radio signal received from the cell via the antenna 31 and the radio processing unit 32 for each cell in which the radio terminal 12 is located at regular intervals or irregularly. Execute. At that time, the control unit 34 measures, for example, the power of the received radio signal, the signal-to-noise ratio, or the signal-to-interference noise ratio as the quality of the radio signal.

Further, the control unit 34 determines whether or not to change the standby cell by comparing the quality of the radio signal for each cell where the radio terminal 12 is located. For example, the control unit 34 determines to change the standby cell when the quality of the radio signal of another cell is better than the quality of the radio signal of the current standby cell.

Further, the control unit 34 performs processing related to the Resume function, for example, processing such as transition from RRC Connected state to RRC Inactive state or vice versa, and processing restarting when the wireless terminal 12 is in RRC Inactive state. Execute. Furthermore, when the radio terminal 12 is in RRC 回線 Inactive state and the standby cell is changed, the control unit 34 executes processing related to taking over the line setting information.

FIG. 7 is an operation flowchart of the wireless terminal 12 regarding the takeover processing of the line setting information.

The control unit 34 determines whether or not to change the standby cell by comparing the quality of the radio signal of the current standby cell and the quality of the radio signal of another cell in which the wireless terminal 12 is located (step S401). ). When determining that the standby cell is not changed (step S401—Yes), the control unit 34 maintains the current standby cell (step S402).

On the other hand, when the control unit 34 determines to change the standby cell (step S401—Yes), the control unit 34 determines whether or not the wireless terminal 12 is in the RRC Inactive state (step S403). If the radio terminal 12 is not in the RRC Inactive state (step S403-No), the control unit 34 changes the standby cell to another cell whose radio signal quality is better than the radio signal quality of the current standby cell. Change (step S404).

On the other hand, if the wireless terminal 12 is in the RRC “Inactive state” (step S403—Yes), the control unit 34 generates a message “1” of the random access procedure including the RA preamble. Then, the control unit 34 refers to the broadcast information from the cell to be changed, and transmits Message 1 by PRACH to the target base station that provides the cell via the radio processing unit 32 and the antenna 31 (step S1). S405).

Thereafter, when the control unit 34 receives the Message 2 of the random access procedure from the target base station via the antenna 31 and the wireless processing unit 32, the control unit 34 includes the Resume ID1 and the identification information of the source base station. Is generated. Then, the control unit 34 transmits the message 3 to the target base station via the wireless processing unit 32 and the antenna 31 (step S406).

Thereafter, when the control unit 34 receives Message 4 of the random access procedure from the target base station via the antenna 31 and the wireless processing unit 32, the control unit 34 extracts Resume ID2 included in the Message 4. And the control part 34 preserve | saves Resume ID2 in the memory | storage part 33 (step S407).
After step S402, S404, or S407, the control unit 34 ends the operation of the wireless terminal 12 related to the line setting information takeover process.

As described above, when a radio terminal that is in RRC Inactive state changes the standby cell, the radio terminal provides a source that provides the current standby cell to the target base station that provides the destination standby cell. The base station identification information and Resume ID are transmitted. The target base station refers to the identification information of the source base station, transmits the Resume ID to the source base station, and inquires the line setting information corresponding to the Resume ID. When the target base station receives the channel setting information from the source base station, the target base station establishes a communication channel with the core network for the wireless terminal using the channel setting information and assigns a Resume ID to the wireless terminal. The target base station stores the assigned Resume ID and the line setting information in association with each other, and notifies the assigned Resume ID to the wireless terminal. As a result, this wireless communication system changes the line setting information maintained for the wireless terminal even when the standby cell is changed during the period in which the wireless terminal is in the RRC-inactive state and has stopped communication. To the target base station that provides the cell. Therefore, this wireless communication system can change the standby cell and maintain the communication line between the base station and the core network without the wireless terminal once returning to RRC Connected state. Therefore, this radio communication system can reduce the number of signaling when changing the standby cell and suppress the power consumption of the radio terminal.

According to the modification, in the line setting information takeover process, the wireless terminal may transmit the identification information of the source base station and Resume ID1 to the target base station after the random access procedure is completed. The target base station may notify ResumeReID2 to the wireless terminal after the random access procedure is completed.

According to another variant, the base station is divided into an aggregation station (Central Unit, CU) that processes radio signals and a distribution station (Distributed Unit, DU) that transmits or receives radio signals. It may be formed according to Cell identification information may be assigned to each DU. Further, for each CU, a RAN area may be set so as to include a DU connected to the CU, and identification information (RAN area ID) of the RAN area may be assigned to each CU. RAN area ID is another example of base station identification information.

FIG. 8 is a schematic configuration diagram of a radio communication system according to this modification. The wireless communication system 2 includes two CUs 14-1 and 14-2, four DUs 15-1 to 15-4, a wireless terminal 12, and an upper node 13. The DU 15-1 and DU 15-2 are connected to the CU 14-1, while the DU 15-3 and DU 15-4 are connected to the CU 14-2. That is, the CU 14-1, the DU 15-1, and the DU 15-2 form one base station, and the CU 14-2, the DU 15-3, and the DU 15-4 form another base station.
The radio communication system 2 according to this modification is different in the configuration of the base station from the radio communication system 1 according to the above embodiment. Therefore, in the following, the configuration of the base station and related parts will be described.

Also in this modification, the number of CUs included in the wireless communication system 2 is not limited to two, and the wireless communication system 2 may include three or more CUs. Similarly, the wireless communication system 2 may include two, three, or five or more DUs. The number of DUs connected to one CU is not limited to two, and may be one or three or more. Further, the wireless communication system 2 may include a plurality of wireless terminals 12 or a plurality of upper nodes 13. Further, when the wireless communication system 1 includes a plurality of upper nodes 13, the upper node to which the CU 14-1 is connected may be different from the upper node to which the CU 14-2 is connected. Further, the wireless terminal 12 may be a mobile terminal or a fixed communication device.

The CU 14-1 and CU 14-2 and the DUs 15-1 to 15-4 relay communication between the wireless terminal 12 and the upper node 13, respectively. For this purpose, the CU 14-1 and the CU 14-2 are connected to the upper node 13 according to a predetermined communication standard defined for communication between the upper node 13 and the base station, for example, an S1 interface. In addition, the CU 14-1 and the CU 14-2 may be connected to each other or to another base station according to a predetermined communication standard defined for communication between base stations, such as an X2 interface.

Further, the CU 14-1, the DU 15-1, and the DU 15-2 are connected through, for example, an optical communication line. Similarly, the CU 14-2, the DU 15-3, and the DU 15-4 are connected through, for example, an optical communication line. In this modification, a unique RAN area ID is assigned to each of the CU 14-1 and CU 14-2. Hereinafter, for convenience, it is assumed that the RAN area ID assigned to the CU 14-1 is RAN area ID 1, and the RAN area ID assigned to the CU 14-2 is RAN area ID 2. The RAN area ID1 assigned to the CU 14-1 is broadcast from the DU 15-1 or DU 15-2 via the broadcast channel. Similarly, the RAN area ID2 assigned to the CU 14-2 is broadcast from the DU 15-3 or DU 15-4 via the broadcast channel.

Each of the DUs 15-1 to 15-4 provides one or more cells, and when the wireless terminal 12 is located in a cell provided by the DU, the wireless terminals 12 can communicate with each other wirelessly.

For example, when the wireless terminal 12 is located in a cell set by the DU 15-1, the wireless terminal 12 can wirelessly communicate with the CU 14-1 via the DU 15-1. Then, the CU 14-1 executes a procedure for setting a radio channel and a procedure for setting an upper channel such as a random access procedure and context setup with the radio terminal 12 capable of radio communication. Thereafter, the CU 14-1 receives a communication signal addressed to the wireless terminal 12 from the upper node 13, and transmits the communication signal to the wireless terminal 12 as a downlink wireless signal via the DU 15-1. Further, the CU 14-1 receives an uplink radio signal from the radio terminal 12 via the DU 15-1, extracts a communication signal included in the radio signal to another communication device (not shown), The communication signal is transmitted to the node 13.

Further, when the wireless terminal 12 is located in either the cell provided by the DU 15-1 or the cell provided by the DU 15-2 and the CU 14-1 is a source base station, the CU 14-1 While 12 is RRC connected state, a process related to Resume setting is executed. That is, the CU 14-1 adds Resume ID to the line setting information related to the wireless terminal 12 so that the wireless terminal 12 can use the Resume function. Then, the CU 14-1 stores the line setting information together with the corresponding Resume ID. Further, the CU 14-1 sets the Resume ID to DU15-1 or DU15 while the wireless terminal 12 continues the wireless communication with the CU14-1, that is, while the wireless terminal 12 is in the RRC Connected state. -2 to the wireless terminal 12 via -2. Similarly, when the wireless terminal 12 is located in any cell set by the CU 14-2 and the CU 14-2 becomes a source base station, the CU 14-2 includes Resume in the line setting information regarding the wireless terminal 12. Add an ID. Then, the CU 14-2 stores the line setting information together with the corresponding Resume ID. Further, the CU 14-2 notifies the wireless terminal 12 of the Resume ID via the DU 15-3 or DU 15-4 while the wireless terminal 12 is in the RRC connected state.

Thereafter, when the wireless terminal 12 determines to change the standby cell, the CU 14-1 and the CU 14-2 execute a process related to taking over the line setting information.

FIG. 9 is a sequence diagram of processing relating to handover of line setting information according to this modification. In this example, it is assumed that the CU 14-1 is a source CU and the CU 14-2 is a target CU. The source CU is an example of a source base station, and the target CU is an example of a target base station. Furthermore, the wireless terminal 12 sets the cell provided by the DU 15-1 as a standby cell when the local station enters the RRC state “Inactive state”. Also, Resume ID assigned to the line setting information of the wireless terminal 12 by the CU 14-1 is Resume ID1, and Resume ID assigned by the CU 14-2 to the line setting information of the wireless terminal 12 is Resume ID2.

After the line setting for the wireless terminal 12 is performed during the RRC connected state, and Resume ID1 is assigned to the line setting information, the wireless terminal 12 proceeds to RRC Inactive state (step S501).

After transitioning to RRC Inactive state, the radio terminal 12 keeps the radio quality of the current standby cell set by the DU 15-1 connected to the CU 14-1 and the radio quality of cells set by other DUs constant. Measure periodically or irregularly. If the wireless terminal 12 determines that the wireless quality of the cell set by another DU is better than the wireless quality of the current standby cell, the wireless terminal 12 determines to reselect the cell (step S502). Then, the radio terminal 12 changes the standby cell from a cell provided by the DU 15-1 to a cell provided by another DU.

When the radio terminal 12 determines to reselect the cell, the RAN area ID of the RAN area to which the DU that provides the standby cell after the change belongs is the RAN area ID of the RAN area to which the DU that provides the standby cell before the change belongs. Determine if they are different. If the RAN area ID is different before and after the standby cell is changed, the wireless terminal 12 executes RAN area update (step S503). Then, the wireless terminal 12 stores the RAN area ID (RAN area ID 2 in this example) for the RAN area to which the DU providing the changed standby cell belongs.

After the RAN area update, the wireless terminal 12 executes a random access procedure for the target CU 14-2. That is, the radio terminal 12 transmits Message 含む 1 including the RA preamble to the CU 14-2 via the DU 15-3 or DU 15-4 using the PRACH radio resource (step S504). Upon detecting the RA preamble, the CU 14-2 transmits an RA response as response information to the wireless terminal 12 via the DU 15-3 or DU 15-4 as Message 2 (step S505). The wireless terminal 12 refers to the TA information included in the RA response and establishes strict synchronization with the CU 14-2 in terms of time. Then, the wireless terminal 12 receives the UL Scheduling Grant from the CU 14-2.

The wireless terminal 12 uses the resource indicated by UL Scheduling Grant, DU15-3 or DU15-4 with Message 3 including Resume ID1 and RAN area ID1 of CU14-1 as the source CU together with the connection request signal. To the CU 14-2 (step S506).

When the CU 14-2 receives the Message 3 including the Resume ID 1 and the RAN area ID 1, the CU 14-2 refers to the RAN area ID 1 and transmits the Resume ID 1 to the CU 14-1 to inquire the line setting information of the wireless terminal 12 (step S507). ). When the CU 14-1 and the CU 14-2 are connected to each other via the X2 interface, the CU 14-2 directly sends Resume ID1 and RAN area ID1 to the CU 14-1 without going through the upper node 13. You may send it. On the other hand, when the CU 14-1 and the CU 14-2 are connected to different upper nodes, the CU 14-2 transmits Resume 及び ID1 and RAN area ID1 to the CU 14-1 via the upper node.

Upon receiving Resume１４ID1 and RAN area ID1 assigned to the wireless terminal 12 from the CU 14-2, the CU 14-1 returns the line setting information of the wireless terminal 12 stored in association with the Resume ID1 to the CU 14-2 ( Step S508). At this time, if the CU 14-1 and the CU 14-2 are connected to each other via the X2 interface, the CU 14-1 directly transmits the line setting information to the CU 14-2 without going through the upper node 13. May be. On the other hand, when CU 14-1 and CU 14-2 are connected to different upper nodes, CU 14-1 transmits line setting information to CU 14-2 via the upper node.

Further, the CU 14-1 executes processing for releasing the upper line set for the wireless terminal 12 (step S509). Further, the CU 14-1 also releases Resume ID1 assigned to the wireless terminal 12 (step S510).

On the other hand, when receiving the line setting information of the wireless terminal 12 from the base station 11-1, the CU 14-2 assigns Resume ID2 to the wireless terminal 12 (step S511). The CU 14-2 stores the Resume ID2 along with the line setting information of the wireless terminal 12. Further, the CU 14-2 establishes a connection of a communication line (that is, an upper line) with the upper node 13 for the wireless terminal 12 based on the line setting information of the wireless terminal 12 (step S512). Then, the CU 14-2 transmits the Message 4 of the random access procedure including the Resume ID 2 to the wireless terminal 12 via the DU 15-3 or DU 15-4 (Step S513). The wireless terminal 12 stores the notified Resume ID2. Then, the CU 14-1, the CU 14-2, and the wireless terminal 12 end the line setting information takeover process.

In this modification as well, in the line setting information takeover process, the wireless terminal may transmit RAN area ID1 and Resume ID1 to the target CU after the random access procedure is completed. The target CU may also notify Resume ID2 to the wireless terminal after the random access procedure is completed.

FIG. 10 is a schematic configuration diagram of the CU 14-1. Since the configuration and function of the CU 14-1 can be the same as the configuration and function of the CU 14-2, the CU 14-1 will be described below.

As shown in FIG. 10, the CU 14-1 includes an optical communication interface unit 41, a wired interface unit 42, a storage unit 43, and a control unit 44. The storage unit 43 and the control unit 44 are formed as separate circuits. Alternatively, each of these units may be mounted on the CU 14-1 as one or a plurality of integrated circuits in which circuits corresponding to the respective units are integrated.

The optical communication interface unit 41 has a communication interface circuit for connecting the CU 14-1 to the DU 15-1 and DU 15-2 via an optical communication line. The optical communication interface unit 41 receives various control information (for example, RAN area ID, etc.) received from the control unit 44 and notified via the DU 15-1 or DU 15-2, or a downlink signal to the wireless terminal 12 as an optical signal. The signal is converted into a signal and transmitted to DU15-1 or DU15-2. The optical communication interface unit 41 receives an optical signal including an uplink signal from the wireless terminal 12 from the DU 15-1 or DU 15-2, converts the optical signal into an electrical signal, and then passes the optical signal to the control unit 44. .

The wired interface unit 42 has a communication interface circuit for connecting the CU 14-1 to the upper node 13 and other base stations or other CUs. Then, the wired interface unit 42 analyzes the signal received from the upper node 13 according to the S1 interface, and extracts a downlink signal, a control signal, and the like included in the signal. Further, the wired interface unit 42 analyzes a signal received from another base station or another CU according to the X2 interface, and extracts a control signal, line setting information, RAN area ID, or the like included in the signal. The wired interface unit 42 passes the extracted downlink signal and control signal to the control unit 44.

On the other hand, the wired interface unit 42 converts the uplink signal received from the control unit 44 into a signal in a format according to the S1 interface, and then outputs the signal to the upper node 13. The wired interface unit 42 converts a control signal, line setting information, or RAN area ID transmitted to another base station or another CU into a format according to the X2 interface. The wired interface unit 42 outputs (or transmits or notifies) the control signal and the like to another base station or another CU.

The storage unit 43 includes, for example, a rewritable nonvolatile semiconductor memory or volatile semiconductor memory. The storage unit 43 stores various information for communicating with the wireless terminal 12, various information transmitted or received by the CU 14-1, and various programs operating on the CU 14-1. In the present embodiment, the storage unit 43 stores the line setting information and the Resume ID for the wireless terminal connected to the own station. Further, the storage unit 43 stores the RAN area ID set in the own station.

The control unit 44 includes, for example, one or a plurality of processors and their peripheral circuits. And the control part 44 performs radio | wireless resource control among the processes for communicating with the radio | wireless terminal 12. FIG. Furthermore, the control unit 44 performs processing of several layers above the physical (PHY) layer, Media Access Control (MAC) layer, Radio Link Control (RLC) layer, and Packet Data Convergence Protocol (PDCP) layer. Execute. For example, the control unit 44 executes processing of all or part of the MAC layer (for example, encryption), the RLC layer, and the PDCP layer. Alternatively, the control unit 44 may execute processing of the RLC layer and the PDCP layer, or may execute processing of the PDCP layer.

Further, the control unit 44 adds Resume ID to the line setting information obtained by performing the line setting process for the wireless terminal 12.

Further, when the CU 14-1 takes over the line setting information from another CU (for example, CU 14-2) as the target CU for the wireless terminal 12, the control unit 44 executes the processing of the target CU in the line setting information takeover process. To do. At that time, the control unit 44 may operate according to the operation flowchart shown in FIG. However, in this case, in step S201, the control unit 44 may determine whether or not RAN area ID1 is included instead of the identification information of the source base station. Further, in step S203, the control unit 44 may identify the source CU with reference to RAN area ID1.

Further, when the CU 14-1 takes over the line setting information to another CU (for example, CU 14-2) as the source CU for the wireless terminal 12, the control unit 44 executes the source CU process in the line setting information takeover process. To do. At that time, the control unit 44 may operate according to the operation flowchart shown in FIG.

FIG. 11 is a schematic configuration diagram of the DU 15-1. Since the configurations and functions of DU15-1 to DU15-4 can be the same as each other, DU15-1 will be described below. The DU 15-1 includes an antenna 51, a wireless processing unit 52, an optical communication interface unit 53, a storage unit 54, and a control unit 55. The wireless processing unit 52, the storage unit 54, and the control unit 55 are formed as separate circuits. Alternatively, each of these units may be mounted on the DU 15-1 as one or a plurality of integrated circuits in which circuits corresponding to the respective units are integrated.

The antenna 51 and the wireless processing unit 52 have the same configuration and function as the antenna 21 and the wireless processing unit 22 of the base station 11 according to the above-described embodiment shown in FIG. Therefore, for details of the antenna 51 and the wireless processing unit 52, refer to the description of the antenna 21 and the wireless processing unit 22.

The optical communication interface unit 53 has a communication interface circuit for connecting the DU 15-1 to the CU 14-1 via an optical communication line. Then, the optical communication interface unit 53 receives the optical signal including various control information (for example, RAN area ID, etc.) notified via the DU 15-1 or the downlink signal to the wireless terminal 12 received via the optical communication line. Is converted into an electrical signal and then passed to the control unit 55. The optical communication interface unit 53 receives an uplink signal from the wireless terminal 12 from the control unit 55, converts it into an optical signal, and transmits the optical signal to the CU 14-1.

The storage unit 54 includes, for example, a rewritable nonvolatile semiconductor memory or volatile semiconductor memory. The storage unit 54 stores various information for communication with the wireless terminal 12 (for example, cell identification information provided by the own station), various information transmitted or received by the DU 15-1, and the DU 15-1. Stores various programs that run.

The control unit 55 includes, for example, one or a plurality of processors and their peripheral circuits. The control unit 55 executes processing of a layer that is not executed by the control unit 44 of the CU 14-1 among the PHY layer, the MAC layer, the RLC layer, and the PDCP layer. For example, when the control unit 44 executes processing of the MAC layer, the RLC layer, and the PDCP layer, the control unit 55 executes processing of the PHY layer. Alternatively, when the control unit 44 performs processing of a part of the MAC layer, the RLC layer, and the PDCP layer, the control unit 55 performs processing of another part of the PHY layer and the MAC layer (for example, retransmission control). To do. Alternatively, when the control unit 44 executes processing of the RLC layer and the PDCP layer, the control unit 55 executes processing of the PHY layer and the MAC layer. Alternatively, when the control unit 44 executes PDCP layer processing, the control unit 55 executes PHY layer, MAC layer, and RLC layer processing.

The wireless terminal 12 according to this modification has the same configuration as the wireless terminal 12 according to the above-described embodiment shown in FIG. However, the wireless terminal 12 according to this modification is different from the procedure shown in FIG. 7 in part of the procedure related to the line setting information takeover process.

FIG. 12 is an operation flowchart of the wireless terminal 12 regarding the line setting information takeover process according to this modification. The control unit 34 of the wireless terminal 12 shown in FIG. 6 executes line setting information takeover processing according to this operation flowchart.

The control unit 34 determines whether or not to change the standby cell by comparing the quality of the radio signal of the current standby cell and the quality of the radio signal of another cell in which the wireless terminal 12 is located (step S601). ). When determining that the standby cell is not changed (step S601-Yes), the control unit 34 maintains the current standby cell (step S602).

On the other hand, when the control unit 34 determines to change the standby cell (step S601-Yes), the control unit 34 determines whether or not the wireless terminal 12 is in the RRC Inactive state (step S603). If the radio terminal 12 is not in the RRC Inactive state (step S603-No), the control unit 34 changes the standby cell to another cell whose radio signal quality is better than the radio signal quality of the current standby cell. Change (step S604).

On the other hand, if the wireless terminal 12 is in the RRC Inactive state (step S603-Yes), the control unit 34 compares the RAN area ID for the RAN area to which each standby cell before and after the change belongs, and compares the RAN area update. It is determined whether or not to perform (step S605). If RAN area update is not performed (step S605-No), the RAN area to which the changed standby cell belongs is the same as the RAN area to which the standby cell before the change belongs. That is, even if the standby cell is changed, the wireless terminal 12 communicates with the core network via the same CU. Therefore, the control unit 34 executes the process of step S604.

On the other hand, when RAN area update is performed (step S605-Yes), the control unit 34 generates Message 1 of the random access procedure including the RA preamble. Then, the control unit 34 refers to the RAN area ID and the cell ID transmitted from the standby cell to be changed to the target CU connected to the DU that provides the standby cell via the radio processing unit 32 and the antenna 31. Then, Message 1 is transmitted by PRACH (step S606).

After that, when receiving the message 2 of the random access procedure from the target CU via the antenna 31 and the wireless processing unit 32, the control unit 34 generates the message 3 of the random access procedure including the Resume ID1 and the RAN area ID. . Then, the control unit 34 transmits the message 3 to the target CU via the wireless processing unit 32 and the antenna 31 (step S607).

After that, when receiving the Message 4 of the random access procedure from the target CU via the antenna 31 and the wireless processing unit 32, the control unit 34 extracts Resume ID2 included in the Message 4. And the control part 34 preserve | saves Resume ID2 in the memory | storage part 33 (step S608).
After step S602, S604, or S608, the control unit 34 ends the operation of the wireless terminal 12 regarding the line setting information takeover process.

In the wireless communication system according to this modification, when a wireless terminal in RRC Inactive state changes a standby cell, the wireless terminal uses the RAN area to which the changed standby cell belongs to the RAN area to which the standby cell before the change belongs. It is determined whether or not the same. When the RAN area to which the standby cell belongs is changed before and after the change of the standby cell, the wireless terminal provides the standby cell before the change to the target CU connected to the DU that provides the standby cell after the change. Send the RAN area ID and Resume ID of the source CU connected to the DU. The target CU refers to the received RAN area ID, transmits the Resume ID to the source CU, and inquires the line setting information corresponding to the Resume ID. Therefore, the wireless communication system according to this modification also provides the standby cell to which the line setting information maintained for the wireless terminal is changed even when the RAN area to which the standby cell belongs is changed before and after the standby cell is changed. Can be transferred to the target CU connected to the DU.

According to another modification, in the wireless communication system 2 shown in FIG. 8, the RAN area ID may be individually notified to the wireless terminal via a dedicated channel. In this case, even if the radio terminal 12 changes the standby cell, the radio terminal 12 cannot determine whether or not the RAN area to which the DU that provides the standby cell belongs has changed before and after the change. Therefore, in this modification, the target CU connected to the DU that provides the changed standby cell refers to the RAN area ID received from the wireless terminal 12 and determines whether to take over the line setting information.

FIG. 13 is a sequence diagram of processing relating to the handover of line setting information according to this modification. In this example, it is assumed that the CU 14-1 is a source CU (source base station). Further, it is assumed that the target CU (target base station) is either CU 14-1 or CU 14-2. Further, the radio terminal 12 sets the cell provided by the DU 15-1 as a standby cell when the RRC “Inactive” state is reached. Also, Resume ID assigned to the line setting information of the wireless terminal 12 by the CU 14-1 is Resume ID1, and Resume ID assigned by the CU 14-2 to the line setting information of the wireless terminal 12 is Resume ID2.

After the line setting for the wireless terminal 12 is performed during the RRC connected state, and the Resume ID 1 is assigned to the line setting information for the wireless terminal 12, the wireless terminal 12 shifts to RRC Inactive state ( Step S701).

After transitioning to RRC Inactive state, the radio terminal 12 keeps the radio quality of the current standby cell set by the DU 15-1 connected to the CU 14-1 and the radio quality of cells set by other DUs constant. Measure periodically or irregularly. If the wireless terminal 12 determines that the wireless quality of a cell set by another DU is better than the wireless quality of the current standby cell, the wireless terminal 12 determines to reselect the cell (step S702). Then, the radio terminal 12 changes the standby cell from a cell provided by the DU 15-1 to a cell provided by another DU.

After the cell reselection, the wireless terminal 12 executes a random access procedure for the target CU. That is, the radio terminal 12 transmits Message 1 including the RA preamble to the target CU connected to the DU that provides the changed standby cell via the PRACH (step S703). When detecting the RA preamble, the target CU transmits an RA response as response information as Message 2 to the wireless terminal 12 via the DU that provides the changed standby cell (step S704). The wireless terminal 12 refers to the TA information included in the RA response, and establishes strict synchronization in time with the target CU. Then, the wireless terminal 12 receives the UL Scheduling Grant from the target CU.

The wireless terminal 12 provides the standby cell after changing the message 3 including the connection request signal, the Resume ID1 and the RAN area ID1 of the source CU 14-1 using the resource indicated by UL Scheduling Grant. To the target CU via the DU (step S705).

When the target CU receives Message 3 including Resume ID1 and RAN area ID1, whether to change Resume by checking whether the received RAN area ID1 matches the RAN area ID assigned to itself. It is determined whether or not (step S706). When the received RAN area ID 1 matches the RAN area ID assigned to the own station, that is, when the target CU connected to the DU providing the changed standby cell is the CU 14-1, the target CU Does not change Resume. That is, since the target CU and the source CU are the same, line setting information is not taken over.

On the other hand, if the received RAN area ID1 is different from the RAN area ID assigned to the own station, the target CU determines to change the resume. That is, since the target CU is different from the source CU, the line setting information from the source CU to the target CU is taken over. Therefore, the target CU and the source CU execute the processes of steps S707 to S712. Note that the processing from step S707 to step S712 is the same as the processing from step S507 to step S512 in the sequence shown in FIG. 9, and thus the description of the processing from step S707 to step S712 is omitted here.

After the communication line between the target CU and the core network is established in step S712, the target CU generates Message 4 of the random access procedure including Resume ID2 and RAN area ID2 assigned to the own station. Then, the target CU transmits the Message 4 to the wireless terminal 12 via the DU that provides the changed standby cell (step S713). The wireless terminal 12 stores the notified Resume ID2. Then, the source CU, the target CU, and the wireless terminal 12 end the line setting information takeover process.

In this modification as well, in the line setting information takeover process, the wireless terminal may transmit RAN area ID1 and Resume ID1 to the target CU after the random access procedure is completed. The target CU may also notify Resume ID2 to the wireless terminal after the random access procedure is completed. However, in this example, when the target CU and the source CU are the same, ResumeCUID2 is not notified from the target CU to the wireless terminal. Therefore, for example, if the Resume ID2 is not notified after a certain period of time has passed since the RAN area ID1 and Resume ID1 are transmitted to the target CU, the wireless terminal determines that the line setting information has not been taken over. May be.

FIG. 14 is an operation flowchart of the target CU in the line setting information takeover process according to this modification.

The control unit 44 of the target CU determines whether the message 3 of the random access procedure received from the wireless terminal 12 includes the Resume ID1 assigned to the wireless terminal 12 by the source base station and the RAN area ID1 assigned to the source CU. (Step S801). If Resume ID1 and RAN area ID1 are not included (step S801-No), the control unit 44 continues the random access procedure for the wireless terminal 12. Then, the control unit 44 generates a RACH Message 4 that does not include the Resume ID, and transmits the Message 4 to the wireless terminal 12 via the DU that provides the changed standby cell (step S802).

On the other hand, if Resume ID1 and RAN area ID1 are included (step S801-Yes), the control unit 44 determines whether RAN area ID1 is different from the RAN area ID assigned to the own station (step S803). . When the RAN area ID1 matches the RAN area ID assigned to the own station (step S803-No), the source CU and the target CU are the same, so the line setting information regarding the wireless terminal 12 is not taken over. Therefore, the control unit 44 executes the process of step S802.

On the other hand, when the RAN area ID1 is different from the RAN area ID assigned to the own station (step S803-Yes), the target CU is different from the source CU. Therefore, the control unit 44 executes the processes of steps S804 to S808. Note that the processing in steps S804 to S808 is basically the same as the processing in steps S203 to S207 in the operation flowchart shown in FIG. Therefore, a detailed description of the processing in steps S804 to S808 is omitted. However, in step S804, RAN area ID1 is referred to as the identification information of the source base station.
After step S802 or step S808, the control unit 44 ends the operation of the target CU regarding the line setting information takeover process.
Note that the control unit 44 may generate Message 4 including Resume ID1 in step S802 and transmit the Message 4 to the wireless terminal 12.

FIG. 15 is an operation flowchart of the wireless terminal in the line setting information takeover process according to this modification.

The control unit 34 determines whether or not to change the standby cell by comparing the quality of the radio signal of the current standby cell and the quality of the radio signal of another cell in which the wireless terminal 12 is located (step S901). ). When it is determined that the standby cell is not changed (step S901-Yes), the control unit 34 maintains the current standby cell (step S902).

On the other hand, when the control unit 34 determines to change the standby cell (step S901-Yes), the control unit 34 determines whether or not the wireless terminal 12 is in the RRC Inactive state (step S903). If the radio terminal 12 is not in the RRC Inactive state (step S903-No), the control unit 34 changes the standby cell to another cell whose radio signal quality is better than the radio signal quality of the current standby cell. Change (step S904).

On the other hand, if the wireless terminal 12 is in the RRC “Inactive state” (step S903—Yes), the control unit 34 generates a message “1” of the random access procedure including the RA preamble. Then, the control unit 34 refers to the broadcast information from the standby cell at the change destination, and sends a message 1 to the target CU connected to the DU providing the cell via the radio processing unit 32 and the antenna 31 using the PRACH. Is transmitted (step S905).

After that, when receiving the message の 2 of the random access procedure from the target base station via the antenna 31 and the wireless processing unit 32, the control unit 34 generates the message 3 of the random access procedure including Resume ID1 and RAN area ID1. . Then, the control unit 34 transmits the message 3 to the target CU via the wireless processing unit 32 and the antenna 31 (step S906).

Thereafter, when receiving the Message 4 of the random access procedure from the target CU via the antenna 31 and the wireless processing unit 32, the control unit 34 determines whether or not Resume ID2 is included in the Message 4 (Step S907). If Resume ID2 is included in Message 4 (step S907—Yes), the control unit 34 extracts Resume ID2 from Message 4. And the control part 34 preserve | saves Resume ID2 in the memory | storage part 33 (step S908). Thereafter, the control unit 34 uses Resume ID2 when resuming communication. On the other hand, if Resume ID2 is not included in Message 4 (step S907—No), the control unit 34 continuously uses Resume ID1 (step S909).
After step S902, S904, S908, or S909, the control unit 34 ends the operation of the wireless terminal 12 regarding the line setting information takeover process.

In step S907, the control unit 34 may execute the process of step S909 even when Resume IV ID1 is included in the received Message IV4.

According to this modified example, even when the identification information of the RAN area is individually notified to the wireless terminal, the wireless communication system uses the line setting information as necessary when the wireless terminal changes the standby cell. To the target CU. Therefore, the wireless communication system can maintain the communication line between the base station and the core network for the wireless terminal even if the standby cell is changed while the wireless terminal is in the RRC / Inactive state.

Note that the wireless communication system 2 shown in FIG. 8 may have a base station (hereinafter simply referred to as a base station) that is not separated into a CU and a DU shown in FIG. In this case, if the base station is the source base station in the takeover processing of the line setting information, the wireless terminal transmits the identification information of the base station, for example, the cell ID, to the target CU together with the Resume ID1 set by the base station do it. Then, the target CU may inquire the channel setting information about the wireless terminal by transmitting Resume ID1 to the source base station specified by the received base station identification information. In addition, when the base station is the target base station in the handover processing of the circuit installation information, the wireless terminal transmits the Resume ID1 set by the source CU and the RAN area ID1 assigned to the source CU to the target base station. Good. Then, the target base station may inquire channel setting information about the wireless terminal by transmitting Resume ID1 to the source CU specified by RAN area ID1.

Note that, in the above-described embodiment or each modification, when the base station that provides the changed standby cell does not support RRC Inactive state, the base station that provides the changed standby cell is a base station for the wireless terminal. The communication line between the station and the core network may be opened. Then, the base station notifies the wireless terminal to that effect, and upon receiving the notification, the wireless terminal may shift to RRC Idle state.

Further, in the above-described embodiment or each modification, the wireless terminal may determine whether to change the standby cell based on the received quality of the wireless signal of each cell.

All examples and specific terms listed herein are intended for instructional purposes to help the reader understand the concepts contributed by the inventor to the present invention and the promotion of the technology. It should be construed that it is not limited to the construction of any example herein, such specific examples and conditions, with respect to showing the superiority and inferiority of the present invention. Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications can be made thereto without departing from the spirit and scope of the present invention.

1, 2 Wireless communication system 11-1, 11-2 Base station 12 Wireless terminal 13 Upper node 14-1, 14-2 CU
15-1 to 15-4 DU
21, 31, 51

Antenna

22, 32, 52

Wireless processing unit

23, 42

Wired interface unit

24, 33, 43, 54

Storage unit

25, 34, 44, 55

Control unit

41, 53 Optical communication interface unit

Claims

A wireless terminal,
A radio processing unit for transmitting a radio signal to any of a plurality of base stations providing a cell, or receiving a radio signal from any of the plurality of base stations;
A communication line between the base station and the core network used for disconnecting a wireless line between the wireless terminal and the plurality of base stations, and for the wireless terminal to communicate via any of the plurality of base stations 1st line identification information for identifying line setting information about a communication line between the base station and the core network when the first state is maintained, and among the plurality of base stations, A storage unit that stores base station identification information for identifying a first base station that provides a cell on which a wireless terminal waits for a wireless signal;
When the radio terminal is in the first state, when changing a cell waiting for a radio signal, the first line identification information and the base station identification information are changed via the radio processing unit. A controller that stores the second channel identification information for identifying the channel setting information transmitted to the second base station that provides the cell and received from the second base station in the storage unit;
A wireless terminal.
The first base station has a distribution station that transmits or receives a radio signal, and an aggregation station that is connected to the distribution station and processes the radio signal,
The wireless terminal according to claim 1, wherein the control unit transmits identification information of the aggregation station included in the first base station to the second base station as the base station identification information.
The control unit executes processing for establishing communication with the second base station according to a random access procedure when changing a cell that waits for a radio signal, and the first line identification information and the second access point in the random access procedure. The wireless terminal according to claim 1, wherein the base station identification information is transmitted to the second base station.
A base station providing a cell,
A radio processing unit that transmits a radio signal to the radio terminal or receives a radio signal from the radio terminal;
A communication interface unit for connecting to an upper node or another base station;
Base station identification information for identifying another base station from the wireless terminal via the wireless processing unit, a wireless line between the wireless terminal and the other base station is disconnected, and the wireless terminal To identify line setting information for the communication line in the first state in which a communication line between the other base station and a core network used for communication via the other base station is maintained. The first line identification information is transmitted to the other base station identified by the base station identification information via the communication interface unit, and the other base station is transmitted. The line setting information corresponding to the first line identification information is received from the communication interface unit, the second line identification information is associated with the line setting information, and the second line identification information is The above And a control unit that transmits to the wireless terminal via the processing unit,
Base station with
The base station according to claim 4, wherein, when receiving the line setting information, the control unit establishes a communication line between the base station and the core network for the wireless terminal using the line setting information.
A storage unit for storing second base station identification information for identifying the base station;
When the base station identification information received from the wireless terminal is different from the second base station identification information, the control unit sends the first line identification to the other base station via the communication interface unit. The base station according to claim 4 or 5, which transmits information.
The control unit receives the base station identification information and the first channel identification information in a random access procedure between the wireless terminal and the base station, and receives the second channel identification information in the random access procedure. The base station according to any one of claims 4 to 6, which notifies the wireless terminal.
A base station providing a cell,
A communication interface unit for connecting to an upper node or another base station;
A wireless line between the wireless terminal and the base station is disconnected, and a communication line between the base station and the core network used for the wireless terminal to communicate via the base station is maintained. A storage unit for storing the line setting information for the communication line in the state of the above in association with the first line identification information;
Upon receiving the first line identification information from another base station via the communication interface unit, a control unit that transmits the line setting information to the other base station via the communication interface unit;
Base station with
When the control unit transmits the line setting information to the other base station, the control unit releases the communication line maintained for the wireless terminal and deletes the first line identification information from the storage unit The base station according to claim 8.
A wireless communication system having a plurality of base stations providing cells and a wireless terminal,
The radio terminal is used for disconnecting a radio channel between the radio terminal and each of the plurality of base stations, and for the radio terminal to communicate via any of the plurality of base stations. When a cell waiting for a radio signal is changed from the first cell to the second cell when the communication line between the network and the core network is maintained in the first state, Base station identification information for identifying a first base station that provides the first cell, and first line identification information for identifying line setting information for the communication line, are provided for the plurality of base stations. Transmitting to a second base station providing the second cell of the
When the second base station transmits the first channel identification information to the first base station and receives the channel setting information from the first base station, the second base station performs second processing on the channel setting information. And associating the second line identification information to the wireless terminal,
Wireless communication system.
When the first base station transmits the line setting information to the second base station, the first base station releases the communication line and the first line identification information for the wireless terminal,
The second base station establishes a communication line between the second base station and the core network for the wireless terminal based on the line setting information received from the first base station. The wireless communication system according to 1.
A wireless communication method in a wireless communication system having a plurality of base stations providing cells and a wireless terminal,
The base station used by the wireless terminal to disconnect a wireless line between the wireless terminal and each of the plurality of base stations, and for the wireless terminal to communicate via any of the plurality of base stations When a cell waiting for a radio signal is changed from the first cell to the second cell when the communication line between the network and the core network is maintained in the first state, Base station identification information for identifying a first base station that provides the first cell, and first line identification information for identifying line setting information for the communication line, are provided for the plurality of base stations. Transmitting to a second base station providing the second cell of the
Transmitting the first line identification information to the first base station by the second base station;
The first base station transmits the line setting information corresponding to the first line identification information to the second base station,
The second base station associates the second line identification information with the received line setting information and notifies the wireless terminal of the second line identification information.
A wireless communication method.